1. Field of the Invention
The present invention relates to the field of medical devices, in general, and, in particular, to a gas delivery system for use in medical or veterinary procedures which require the introduction of a gas into a human or animal body, or to create or maintain a controlled gas environment. More specifically, the invention is applicable to devices and methods for safely administering gases to patients for insufflation of organs, such as during endoscopic procedures.
2. Related Art
Endoscopy is an important procedure for the effective diagnosis and treatment of many disorders, and is particularly useful in diagnosing and treating various gastrointestinal disorders. Successful inspection of the gastrointestinal tract is dependent upon both the expertise of the physician and the quality of the endoscopic instruments and accessories used in the procedure. Two particular types of endoscopes used in the field of gastroenterology are the gastroscope for upper intestinal visualization, and the colonoscope for the visualization of the colon.
During an endoscopic procedure, the endoscope is attached to a light source to illuminate the area under examination. The endoscope then transmits an image of the inside of a patient's bowel to the physician via either fiber optic bundles or a microchip-based communication system. The endoscope also provides a conduit for the delivery of a gas to insufflate the bowel to facilitate examination. Both light and gas are thus critical to successful completion of all diagnostic or therapeutic endoscopic procedures.
Known endoscopic devices utilize an air compressor which is housed inside a light source to deliver the gas. Limits for the volume and pressure of the delivered gas are pre-set in the compressor at the time it is manufactured. The temperature of the delivered gas is not controlled in known systems, and varies according to the ambient air temperature and any negligible heat which may be generated during compression of the air by the internal air compressor.
Since known systems do not provide a quantitatively accurate system within the light source for accurately regulating the delivery of the gas, there can be large variations in the pressure, volume and temperature of gas administered during an endoscopic procedure. A physician who uses a standard light source during an endoscopic procedure must rely upon the pre-set adjustments of the internal air compressor which, generally, only allows adjustments to settings of "low," "medium," "high" and "off." The instruments are not provided with means to finely calibrate the pressure and volume of the gas. Furthermore, the air compressors of known systems operate by compressing air in a series of spurts or pulses due to reciprocating action, potentially causing unwanted variation in actual pressure delivered. Thus, a physician cannot determine or accurately control the exact volume or pressure of the gas which is being used to insufflate a patient's bowel during the procedure. No instruments are now available to record these variables for documentation in a patient's chart.
Moreover, known gas delivery systems are not provided with a means to control the temperature of the gas delivered to a patient. Under Boyle's and Charles' Laws, it is known that the variables of pressure of a gas in a constant volume is proportional to the temperature of gas. Thus, known systems which do not regulate the temperature of the gas being administered lose thermodynamic control over the performance of the gas delivery system.
It is therefore desirable to provide a gas delivery system in which the pressure, volume, and temperature are all quantitatively controlled, regulated, and capable of being monitored by the physician for the safety of the patient.
It is known that air pressure is a cause of a potentially fatal perforation of a colon during a colonoscopic examination, or may cause the development of late perforations. Dr. R.A. Kozarek et al, in an article entitled "Air Pressure Induccd Colon Injury During Diagnostic Colonscopy," Gastroenterology 78:7-14 (1980) cites that, using four different light sources and determining pressure needed to perforate the colons of dogs, pigs, human cadavers and in vivo human investigation, all four of the light source machines used are capable of delivering pressure that exceed the rupture point in all but the dog's colon. (The dog's colon could not be perforated, possibly because is has two layers of smooth muscle, in contrast to human and pig colons only having one layer of smooth muscle, plus taenia coli.) Therefore, rupture of the human colon is a very real possibility using known light source machines, as the pressure, volume, and temperature of the insufflating gas are not accurately controllable.
For these reasons also, it is desirable to provide a gas delivery system to the endoscopic device in which the delivered gas is reliably regulated so as to minimize possible injury caused by gas.
Another safety factor is the lack of a voltage regulator on the known light sources. Electrical power fluctuations during an endoscopic procedure present a danger to the patient. A power surge may cause the air compressor to function abnormally by putting out transient increased volumes or pressures of the delivered ambient air. If a colonoscope were in a particularly delicate orientation (such as in a diverticulum, in a delicate "slide-by" during the procedure, or in a fixed or partially obstructed loop of bowel), this increased pressure could cause a serosal tear, perforation or sub-mucosal infiltration of gas.
Other phenomena contribute to possible danger to patients. A valsalva maneuver, if performed by the patient during an examination, can increase the pressure in a colon by an average of 38 mm Hg. Furthermore, external pressure exerted by the examining physician to expedite movement of the colonoscope through the bowel can exert up to an average of 17 mm Hg. These pressures are additive to the intraluminal pressure already present in the colon during colonoscopy, so that any pressure component added by the gas delivery system risks pushing the total pressure over a threshold where injury will occur.
Therefore, it is desirable, when using a pressurized gas delivery system, to prevent unwanted transient increases in pressure, as this prevention would guard the safety of the patient.
It is known that the endoscopic use of gas such as ambient air interferes with other diagnostic procedures such as barium enemas which might need to be performed the same day on a patient. Furthermore, just performing a colonoscopic procedure can usually stop fairly brisk diverticular bleeding of the colon, but that, unfortunately, the exact site of bleeding cannot therefore usually be found. This stoppage of diverticular bleeding defeats the purpose of the diagnostic procedure. The cause of this defeat of the diagnostic procedure may be that the insufflation and distention of the bowel lumen with ambient air or a barium examination with cold barium may cause the small bleeding vessels to go into spasm and stop bleeding, perhaps for hours after the examination.
In this case, the reduced usefulness of bleeding scans or arteriograms are due to the amount of air or barium which is left in the gastro-intestinal tract after the examination. If surgery is elected as a subsequent step, a surgeon does not know accurately the point in the bowel where the patient is bleeding. Surgical intervention may result in the removal of an unnecessarily large segment of bowel, or a sub-total colectomy, because of an inadequate diagnostic procedure.
Therefore, it is desirable to use a gas at a controlled volume, pressure and temperature which does not interfere with any diagnostic procedures conducted in conjunction with the gas delivery system.
Although ambient air generally is used when delivering a gas to a patient through a gastroscope or a colonoscope, carbon dioxide (CO.sub.2) gas is used to great advantage as an alternative gas insufflation source when performing a colonoscopy. The advantages of using CO.sub.2 gas for routine colonoscopy are significant. For instance, CO.sub.2 gas reduces the likelihood of an explosion of volatile gas which may be present in the colon when electro-coagulating equipment is used during a procedure. Also, since CO.sub.2 is rapidly absorbed from the intestines in less than one hour after the procedure is performed, it is possible to schedule additional necessary procedures (such as an X-ray, an ultrasound or a CT scan) the same day after the colonoscopy. Presently, this is not the case in the use of ambient air.
The virtual elimination of a potential explosion of a volatile gas in the colon is an advantage which applies both to patients who have not been adequately prepared for an examination, or to those who have inadvertently consumed a fermentable food substance in the time period preceding the colonoscopy. That CO.sub.2 should be used for all colonoscopies is a statement which has been made by some of the leading endoscopists in the world. The logic is not just that the use of CO.sub.2 is a "fire extinguisher." The use of CO.sub.2, as will be discussed in greater detail below, has advantages over insufflation with ambient air for all patients, even for those in whom combustion is not a danger.
Hussein, A.M.J. et al, in an article entitled "Carbon Dioxide Insufflation For More Comfortable Colonoscopy," Gastrointestinal Endoscooy 30:68-70 (1984), documents that patients who receive CO.sub.2 as the sole insufflation gas source have less discomfort and less flatus from the examination. Also, patients reabsorb the CO.sub.2 gas within approximately one-half hour after the examination, facilitating further endoscopic examination or other tests such as barium enemas, CT scans, ultra-sound tests or arteriograms. These tests can be performed the same day as the colonscopy.
The use of CO.sub.2 also provides benefits in the field of radiology as well as for colonoscopy. Patient comfort, fast reabsorption and adequacy as a gas source for double-contrast barium enema studies are included. CO.sub.2 is inexpensive and is sterile. It causes less discomfort during and after a colonoscopic procedure, as evidenced by a study of over 5000 colonoscopy patients by B. H. Rogers, M.D., reported in Gastrointestinal Endoscooy 31:108-9 (1985). Other articles cite no contraindication in the use of CO.sub.2 in patients with serious lung disease. Studies monitoring arterial blood gas confirm the safety of this gas for colonoscopic examination in patients even with lung disease.
Significantly, the use of CO.sub.2 increases blood flow to the colon, and increases the amount of pO.sub.2 in the perivascular areas, apparently due to the dissociation of the oxy-hemoglobin curve in the colonic mucosa. Ambient air, on the other hand, which comprises 80% nitrogen, causes both increased and sustained intraluminal pressure and significantly decreases blood flow to the colon. As noted by Christopher B. Williams, increased blood flow to the colon, using CO.sub.2, may facilitate determination of the source and potentiate endoscopic treatment of lower gastro-intestinal bleeding in patients with diverticular or arterial-venous malformations.
Therefore, it is desirable to use a gas which has minimal detrimental and undesirable physiologic effects, so that the patient is examined and treated under physiologic, or near-physiologic, conditions.
Even if CO.sub.2 is presently used in a procedure using the known delivery system, certain shortcomings exist. These include poorly controlled pressure and volume regulators, clumsy manual irrigation of the distal lens system, awkward placement of the CO.sub.2 button on the colonoscope, inadvertent injection of small metal flakes from the CO.sub.2 cylinder into the colonoscope's insufflation tubing, potential freeze-up of the CO.sub.2 valve nozzle, fluctuation of CO.sub.2 gas pressure (sputtering), accidental injection of liquid CO.sub.2 into the colonoscope itself, or, potentially, into the patient.
In known CO.sub.2 delivery systems, the CO.sub.2 is administered by connecting an external CO.sub.2 gas cylinder pressure regulator, via plastic tubing, directly to a CO.sub.2 insufflation valve device on the colonoscope. However, since the CO.sub.2 insufflation valve is not conveniently located on the colonoscope, it is awkward to use by the physician performing the procedure. With the use of the inventive device (described below), the CO.sub.2 valve is no longer required. CO.sub.2 now passes through the usual air insufflation pathway, thus bypassing the air compressor.
Further, CO.sub.2 gas delivered in the known delivery manner during a colonoscopy is not regulated by the internal gas compressor of the light source as it would if ambient air were being employed. The physician must manually adjust the pressure valve settings on the CO.sub.2 cylinder itself, leaving many inherent possibilities for error due to imprecise pressure gauges and volume regulators on the CO.sub.2 cylinder.
Of particular concern, even when a CO.sub.2 gas source is employed, is the lack of any means to control its temperature. Without temperature control, the volume and/or the pressure of the insufflated gas will increase after the gas has entered the lumen of the bowel due to heating of the gas by the body itself. This is non-physiologic and potentially harmful to the patient. As in systems where ambient air is employed, insufficient control over the gas temperature, pressure, and volume can cause over-distension or even perforation of the bowel.
Thus, a need exists for a system and method for administering gas to a human or animal body which provides a means to accurately determine and control the temperature, volume and pressure of the gas being delivered to the patient. It is desirable that the system be both comfortable in its use for the physician, and also use the standard air insufflation pathway without using the light source air compressor. Determination and control of all three of these parameters constitutes determination and control of three independent variables in Boyle's and Charles' Laws.
Currently, upper endoscopy has no means to use CO.sub.2 for insufflation. An accurate control system would make it possible to use CO.sub.2 gas when performing upper endoscopy, which has many of the same advantages discussed for colonoscopy.
More generally, a need exists for a system which overcomes the above-described limitations, whether CO.sub.2 or another gas is used for insufflation.